linux-kernel - Re: [PATCH] memory-hotplug: Fix bad area access on dissolve_free_huge

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Message-ID: <20160921120507.GG10300@dhcp22.suse.cz>
Date:   Wed, 21 Sep 2016 14:05:08 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     Rui Teng <rui.teng@...ux.vnet.ibm.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Santhosh G <santhog4@...ibm.com>
Subject: Re: [PATCH] memory-hotplug: Fix bad area access on
 dissolve_free_huge_pages()

On Tue 20-09-16 10:43:13, Dave Hansen wrote:
> On 09/20/2016 08:52 AM, Rui Teng wrote:
> > On 9/20/16 10:53 PM, Dave Hansen wrote:
> ...
> >> That's good, but aren't we still left with a situation where we've
> >> offlined and dissolved the _middle_ of a gigantic huge page while the
> >> head page is still in place and online?
> >>
> >> That seems bad.
> >>
> > What about refusing to change the status for such memory block, if it
> > contains a huge page which larger than itself? (function
> > memory_block_action())
> 
> How will this be visible to users, though?  That sounds like you simply
> won't be able to offline memory with gigantic huge pages.

I might be missing something but Is this any different from a regular
failure when the memory cannot be freed? I mean
/sys/devices/system/memory/memory API doesn't give you any hint whether
the memory in the particular block is used and
unmigrateable.

-- 
Michal Hocko
SUSE Labs